If long exposure astrophotography is carried out with a fixed camera, added light of stars during a long exposure form straight or curved light trails in the captured image because celestial objects move relative to the camera due to the earth's rotation (diurnal motion). To carry out a long exposure in order to photograph a celestial object so that the celestial object appears to be still (a luminous point), an equatorial equipped with an auto tracking system is generally used.
In recent years, a method has been proposed in which a celestial object(s) is photographed a plurality of times with a fixed digital camera without using an equatorial, and thereafter, the images thus obtained at the plurality of times are added while correcting the positions of the celestial object(s) using data on the obtained images (Patent Literatures 1 and 2).